Editor's Note: The following piece is part of an occasional series in which Fred Burton, our vice president of intelligence, reflects on his storied experience as a counterterrorism agent for the U.S. State Department.

Having investigated quite a few aircraft disasters as a special agent with the U.S. State Department, including the suspicious crash of a C-130 that killed Pakistani President Muhammad Zia-ul-Haq, U.S. Ambassador Arnold Raphel and U.S. Army Gen. Herbert M. Wassom in 1988, I thought it would be useful to explain the investigative process for downed aircraft. This context will hopefully give clarity to the most recent developments in the case of Flight 9268 that crashed in Egypt on Oct. 31.

According to the BBC, the Airbus A321, operated by the Russian airline Metrojet, took off from Sharm el-Sheikh International Airport at 05:58 (03:58 GMT) on Oct. 31. At 06:14 (04:14 GMT), the plane failed to make scheduled contact with air traffic control based in Larnaca, Cyprus. The plane disappeared from radar screens six minutes later while flying over central Sinai. Egyptian authorities said no SOS calls were received by air traffic controllers, and data released by the flight tracking website Flightradar24 showed that just before the radar signal was lost, the aircraft reached an altitude of more than 33,000 feet (approximately 9,900 meters).

Agents begin aircraft disaster investigations even before the crash debris has been located. They start by ruling out causes of the crash, focusing on four main variables: catastrophic mechanical or electrical failure, pilot error, weather and man-made causes. The last category includes criminal sabotage, terrorism and military activities, such as missiles being fired at the aircraft.

In the case of Flight 9268, by my judgment, the investigators have likely already ruled out pilot error and weather. The fact that the aircraft was already at cruising altitude when radio contact was lost would give the pilots time to correct most errors. At cruising altitude, the pilots would also have time to radio back and report any problems. With the information currently available, catastrophic mechanical failure or man-made causes would be the two initial working theories. And though it is important to keep an open mind until investigations are complete, it is also important to remember that planes at 35,000 feet don't just fall out of the sky without a serious reason.

It is reasonable to assume that the United States and other governments captured a signature — or a picture — of the explosion from satellite coverage as well. These images could provide a good idea of what the aircraft looked like close to the time of the event, similar to the breakup photos of the Space Shuttle Challenger. Behind the scenes, the CIA, FBI and numerous foreign intelligence services will also be beating the bushes, looking for any evidence or chatter of an attack that could have been missed.

From an investigative perspective, the absence of a manual pilot alert may be due to a catastrophic decompression in the pilot cabin that incapacitated the pilots. This could have been caused by a massive structural failure of the aircraft or by an improvised explosive device. The U.K. and U.S. governments have publicly stated that more likely than not, a bomb caused the aircraft to fall from the sky.

The tail section uncovered intact a good distance away from where the front of the plane crashed tells me that in all probability an improvised explosive device was detonated in the cargo hold, exploding by means of a set timing mechanism or barometric device set to detonate at a specific altitude, similar to what we saw in the Lockerbie case.

If it is confirmed that a bomb downed the flight, investigators will be fixated on whether the device was detonated by means of a timing mechanism or by a barometric altitude device. The latter would indicate a sophisticated actor was behind the plot. And ultimately it is more important how the plane went down than why, because how the bomb got into the hold and how it was constructed and hidden will help prevent other attacks from occurring. From a law enforcement perspective, figuring out the why can wait.